1. Field of the Invention
The present invention relates to a thermoplastic composition that comprises a unreacted mixture of polyethylene oxide and a multicarboxylic acid. The thermoplastic composition is capable of being extruded into fibers that may be formed into nonwoven structures that may be used in a disposable absorbent product intended for the absorption of fluids such as body fluids.
2. Description of the Related Art
Disposable absorbent products currently find widespread use in many applications. For example, in the infant and child care areas, diapers and training pants have generally replaced reusable cloth absorbent articles. Other typical disposable absorbent products include feminine care products such as sanitary napkins or tampons, adult incontinence products, and health care products such as surgical drapes or wound dressings. A typical disposable absorbent product generally comprises a composite structure including a topsheet, a backsheet, and an absorbent structure between the topsheet and backsheet. These products usually include some type of fastening system for fitting the product onto the wearer.
Disposable absorbent products are typically subjected to one or more liquid insults, such as of water, urine, menses, or blood, during use. As such, the outer cover backsheet materials of the disposable absorbent products are typically made of liquid-insoluble and liquid impermeable materials, such as polypropylene films, that exhibit a sufficient strength and handling capability so that the disposable absorbent product retains its integrity during use by a wearer and does not allow leakage of the liquid insulting the product.
Although current disposable baby diapers and other disposable absorbent products have been generally accepted by the public, these products still have need of improvement in specific areas. For example, many disposable absorbent products can be difficult to dispose of. For example, attempts to flush many disposable absorbent products down a toilet into a sewage system typically lead to blockage of the toilet or pipes connecting the toilet to the sewage system. In particular, the outer cover materials typically used in the disposable absorbent products generally do not disintegrate or disperse when flushed down a toilet so that the disposable absorbent product cannot be disposed of in this way. If the outer cover materials are made very thin in order to reduce the overall bulk of the disposable absorbent product so as to reduce the likelihood of blockage of a toilet or a sewage pipe, then the outer cover material typically will not exhibit sufficient strength to prevent tearing or ripping as the outer cover material is subjected to the stresses of normal use by a wearer.
Furthermore, solid waste disposal is becoming an ever increasing concern throughout the world. As landfills continue to fill up, there has been an increased demand for material source reduction in disposable products, the incorporation of more recyclable and/or degradable components in disposable products, and the design of products that can be disposed of by means other than by incorporation into solid waste disposal facilities such as landfills.
As such, there is a need for new materials that may be used in disposable absorbent products that generally retain their integrity and strength during use, but after such use, the materials may be more efficiently disposed of. For example, the disposable absorbent product may be easily and efficiently disposed of by composting. Alternatively, the disposable absorbent product may be easily and efficiently disposed of to a liquid sewage system wherein the disposable absorbent product is capable of being degraded.
Polyethylene oxide is a known material and has been used widely in a variety of applications. However, the processing of polyethylene oxide into a fiber, a film, or other extrudable or nonwoven structures has proven to be a significant challenge. This challenging task has been found to be particularly acute when trying to use polyethylene oxide in a fiber making process. Such processing difficulty is due, in part, to the fact that commercially-available polyethylene oxide typically comes in a powder form and is predominately available in high molecular weight versions, typically ranging in a weight average molecular weight from over 100,000 to 8,000,000.
Such a physical form or properties of the polyethylene oxide has been found to negatively impact the processing of the polyethylene oxide in several ways. First, any material, including polyethylene oxide, in a powder form is generally more difficult to process in terms of feeding and extrusion as compared to a material in a pelletized form, such as is typically encountered, for example, with polyolefins. Second, the high molecular weight of the polyethylene oxide typically results in significant entanglement of the polyethylene oxide polymer chains during certain processing techniques, such as extrusion. An extruder being used in such a situation will typically require a very large torque to feed the high molecular weight material through it which typically results in a pronounced "elastic-retraction" property of the molten fiber being processed which generally results in the molten fiber resisting being drawn down as it exits a spinneret attached to the extruder. These factors generally result in a very poor melt strength of the resultant fiber and make fiber spinning impracticable. Third, polyethylene oxide has a very low melting temperature, generally about 65.degree. C., which makes the polyethylene oxide difficult to solidify during quenching and which causes process difficulties due to the stickiness of fiber prepared from the polyethylene oxide.
In addition, polyethylene oxide is generally a water soluble polymer. As such, even if one were able to prepare fibers from polyethylene oxide, such fibers would have a limited usefulness in applications in which the fibers were to be insulted with a liquid such as water, urine, blood, or menses. Thus, it would be desirable to be able to make a fiber comprising polyethylene oxide which was not instantly water soluble but instead exhibited a delayed solubility in, for example, water or other aqueous liquids.
It is therefore an object of the present invention to provide a thermoplastic composition comprising polyethylene oxide which exhibits improved processability properties and desirable solubility properties.
It is also an object of the present invention to provide a thermoplastic composition comprising polyethylene oxide which may be easily and efficiently formed into a fiber.
It is also an object of the present invention to provide a thermoplastic composition comprising polyethylene oxide which is suitable for use in preparing nonwoven structures.
It is also an object of the present invention to provide a fiber or nonwoven structure that is readily degradable in the environment.